Method of repairing damaged holes in a boiler drum

ABSTRACT

Apparatus and methods for repairing or producing openings in a boiler drum is provided. Weld material is applied to the drum in the area of the openings to reduce substantially the size of the openings. A precisely aligned drill within the drum is then radially and longitudinally moved in steps is inserted within the drum and to produce or redimension openings within the drum.

' United States Patent [191 Tarves, Jr.

[ June 26, 1973 METHOD OF REPAIRING DAMAGED HOLES IN A BOILER DRUM 260Erial Road, Blackwood, NJ. 08012 221 Filed: Jan. 28, 1971 211App1.No.:110,404

-[1 1 In en ngtlmesirs. 19-9.- B95. 2 2,

[52] US. Cl. 29/401, 29/157.4, 291527.] [51] Int. Cl 822d 19/10 [58]Field of Search 29/l57.4, 401, 527.1;

[56] References Cited UNITED STATES PATENTS 3,557,435 1/1971 Powell etal. 29/401 /I///I///I/I/ 1,857,912 5/1932 Jones 29/401 X 2,120,5256/1938 Mclierihan 29/401 3,608,173

9/1971 Watson et al 29/1574 Primary Examiner-Charles W. LanharnAssistant Examiner-D. C. Reiley, llI Attorney-Edward M. Farrell [5 7]ABSTRACT Apparatus and methods for repairing or producing openings in aboiler drum is provided. Weld material is applied to the drum in thearea of the openings to reduce substantially the size of the openings. Aprecisely aligned drill within the drum is then radially andlongitudinally moved in steps is inserted within the drum and to produceor redimension openings within the drum.

7 Claims, 13 Drawing Figures PAIENIED 3. 740.820

sum 1 or 4 INVENTOR.

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ATTORNEY Q Q Q 0 ROBERT J.TARVES,JR.

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INVENTO ROBERT J. TARVES,JR, BY

ORNEY METHOD OF REPAIRING DAMAGED HOLES IN A BOILER DRUM In the normalproduction of power, heat energy contained in a fuel is constantlysupplied at one end-and mechanical or electrical power is delivered atthe other end of the system. The principal machine of a power plantwhich converts heat energy into mechanical energy is known as the primemover, which could be a turbine or a reciprocating engine or both. Inmany systems steam is generated in a boiler by burning fuel in afurnace. The steam formed by the vaporization of water in the boilerserves as a heat carrier, which is readily conveyed through pipe linesto the prime movers. In heat power plants, energy is secured by rapidoxidation of some material which may be either in its natural state,such as coal, or different types of fuel.

A steam generating unit includes apparatus for producing, furnishing orrecovering heat, together with apparatus for transferring the heat. Theunit may include a boiler furnace, fuel burning equipment and numerousother items.

Steam generating drums used in most power systems are designed to beused with water levels affording a large steam liberating surface. Alarge number of tubes are connected to openings in the drums to affordmeans to enable the gases to expand and contract and to be applied toother units in the steam generating system.

Repair and replacement of boilers and their associated tubes are oftenrequired as a result of various faults developed in the system orimpurities in the water used. For example, feedwater impuritiesprecipitated during operation of a typical steam generating system mayresultin the formation of scale, corrosion, embrittlement and other illeffects in the boiler drum or associated tubing.

Despite a program of maintenance, scale deposited on the internalsurfaces of the drum and tubes left by the evaporation of water carryingimpurities often cause overheating and weakening of the boiler tubes.Also, corrosion and scale cause overheating as a result of lack of heattransfer causing the tubes to burn out. Also, the corrosion produces awasting away of boiler parts with a corresponding reduction in theirstrength. This is often accompanied by an enlargement or elongation ofthe holes in the boiler.

In the past, overheating causing elongation of the holes in a boilerhave been repaired by the insertion of I copper ferrules to fill in thevoids created by the elongations. This involves removal of the tubes,inserting the ferrules, replacing and expanding the ends of the tubes.However, the use of ferrules has limitations beyond which they are notpermitted or acceptable by regulatory or inspection agencies. The reasonfor this is that ferrules are subject to be blown out as a result of thehigh pressures created within the boiler drum.

When the holes in the boiler drum become enlarged or elongated as aresult of corrosion, overheating or other reasons, the steam generatingsystem operates at reduced pressures and efficiency as a result of theleakage around the openingswhich receive the tubes. This oftennecessitates the condemnation of the boiler drum for steam generatingpurposes. The replacement of such boiler drums involves a heavy outlayof expense for equipment and labor.

It is an object of this invention to provide novel means and methods forrepairing a drum of the type used in steam generating plants.

It is a further object of this invention to provide improved means andmethods for repairing with a minimum amount of expense a drum of thetype used in steam generating plants.

It is still a further object of this invention to provide improved meansand methods for redrilling a plurality of holes in a drum with highprecision and efficiency.

It is still a further object of this invention to provide improvedapparatus for producing openings within a drum.

In accordance with the present invention, apparatus and methods forrepairing a boiler drum is provided. A weld material is added toenlarged corroded openings to provide openings smaller in dimensionsthan the desired sizes. A boring machine is mounted on to a shaft withinthe drum and disposed for rotational and longitudinal movements withinthe drum. A drill on the boring machine is larger than the smalleropenings produced by the excess weld material and dimensioned to thesize of the desired openings. The boring tool is first rotated to drilla set of openings in a row about the circumference of the drum. The toolis then moved in steps longitudinally along the drum. At each step, thetool is moved about the circumference of the drum to drill another setof holes. The sequence is repeated until all the holes in the drum havebeen redrilled. In some cases, holes are rebored in a drum larger thanthe desired sizes with metal rings with the desired inside diametersbeing inserted into the enlarged openings.

Other objects and advantages of the present invention will be apparentand suggest themselves to those skilled in the art, from a reading ofthe following specification and claims, in conjunction with theaccompanying drawings in which:

FIG. 1 is a perspective view, partly broken away and in cross-section,of a portion of a boiler drum and apparatus of the present invention;

FIG. 2 is an end view of the arrangement of FIG. 1, including toolalignment means, in accordance with the present invention;

FIG. 3 is an enlarged view of a portion of the apparatus illustrated inFIG. 2 including the alignment means;

FIG. 4 illustrates an enlarged portion of the assembly shown in FIG. 1;

FIG. 5 is a view taken along lines 4-4 of FIG. 4;

FIG. 6 is a side view of a portion of the apparatus of FIG. 1illustrating various operating positions, in accordance with the presentinvention;

FIGS. 7a, 7b and 7c illustrate steps in the repair of a hole in a druminvolving the addition of weld material;

FIGS. 8a, 8b and 8c illustrate steps in the repair of a drum whichinvolves the addition of metal rings; and

FIG. 9 is a schematic diagram illustrating circuitry for varying thespeed of a machine tool.

In describing one embodiment of the subject invention it is assumed thata boiler drum has been in use and that the openings therein have becomeelongated or enlarged as a result of corrosion, overheating or the like.Instead of replacing the boiler drum with a new drum, the subjectinvention provides the methods and means for repairing the defectivedrum. The first step, not illustrated, involves removing the tubes fromthe openings in the drum. In most cases, new tubes will replace theremoved tubes. It will also be assumed in describing the presentinvention that various reference points are available which areindicative of the center of the drum and positions of the holes to bedrilled. These may inelude lines marked on the drum after variousmeasurements.

Referring to the drawings, a typical boiler drum includes apparatus 12disposed therein. The drum 10 includes a plurality of openings 14 forreceiving a plurality of tubes (not illustrated). FIG. 7a illustrates atypical elongated hole 11 in a drum which must be repaired. FIG. 7billustrates an elongated hole with excess weld material 13 addedtherein. FIG. 70 illustrates a hole 15 with the excess weld materialafter it has been rebored to the desired size.

Weld material is added around the openings in the drum after suitablecleaning which involves removing the corroded material from the drum. Asa result of adding excess weld material, smaller holes are formed in thedrum. The weld material may be added by conventional methods. Thesmaller holes are smaller in area than required to receive the new tubeswhich eventually must be replaced on the drum. 7

After the welding operation, the apparatus 12 is inserted into the drum10 through an opening at the end of the drum (not illustrated). Theapparatus 12 may be inserted through the opening in pieces and thenassembled within the drum. The diameter of the drum 10 is large enoughto permit an operator to enter to perform the repairs on the drum, aswill be described. It may be in the order of three feet in diameter orlarger. One of the features of the present invention relates to themachining of holes within the drum.

The apparatus 12 includes a machine tool 16 adapted to be electricallydriven. The tool includes a drill element 18 dimensioned to the desiredsize of the holes to be drilled in the drum.

The machine tool 16 is supported by supporting means including a maincylindrical tube 20 having a slidable shaft 22 extending therethrough.Details of this arrangement are illustrated in FIGS. 4 and 5. The tube20 is held fixedly in place within the drum 10 by means of a pluralityof legs 24 and 26. The legs 24 and 26, which are spaced from each other,are secured at one end to the tube 20 by any suitable means and extendtoward the inner wall of the drum 10.

The legs 24 and 26 include a plurality of alignment screws 28 and 30,respectively, in threaded engagement with the free ends of the legs. Thealignment screws may be adjusted to assure that the tube 20 is centeredwithin the drum 16 prior to performing a drilling operation. The screws28 and 30 are maintained tightly against the inner wallof the drumduring a drilling operation.

A pair of bearing members 32 and 34 are suitably mounted to the ends ofthe tube 20 and dimensioned to receive the shaft 22 therein. The shaft22 is adapted to be rotated or moved longitudinally within the tube 20.

The shaft 22 is secured to a frame 36for holding the machine tool 16. Atoothed rack 38 is operatively connected to a gear mechanism in ahousing 40. A handle 42 is provided to permit an operator to move thetool 16 radially towards the inner wall of the drum 10 by the engagementof the gear mechanism within the housing with the rack 38. The radialmovement of the tool 16 is illustrated in FIG. 3.

The tool 16 is adapted to be rotated (illustrated in FIG. 2) or movedlongitudinally (illustrated in FIG. 6) within the drum 10 in accordancewiththe movement of the shaft 22. These movements permit the tool 16 tobe properly aligned with a hole to be rebored or drilled. After the tool16 has been aligned and prior to reboring or drilling, a tighteningmechanism 44 including a screw threadedly engaging the top portion 46 ofthe frame 36 is manually adjusted to engage the inner wall of the drumto maintain the boring tool 16 firmly in position as the drillingoperation is being performed.

During operation, an operator, after securing the tool 16 in place,moves the cutting portion of the tool in a radial direction by manuallyturning the handle 42 so that the drill 18 inserted into one of theholes 14 to rebore the hole or, in the case of manufacturing, drill anew hole. After boring or drilling one hole, the tightening means 44 isloosened to permit the tool 16 to be rotated until it is positioned tobore or drill the next hole. The boring or drilling operations arecontinued until all the holes in one row about the circumference of thedrum 10 have been bored or drilled.

Following the boring or drilling of one row of holes about thecircumference of the drum, an'operator then moves the tool 16longitudinally along the axis of the drum to the next row of holes to bedrilled or bored. These steps are repeated until all the holes in thedrum have been bored or drilled. The length of the shaft 22 will limitthe number of rows of holes which can be drilled or bored accuratelybefore the entire apparatus 12 has to be moved because of the tendencyof the shaft to flex if it is too long. However, in some cases, theshaft could extend along the entire length of the drum to eliminate theneed to periodically move the apparatus during a repair operation.

In many cases, the holes to be drilled in the drum are relatively large,in the order of 3 or more inches. This generally requires thatstabilizing means be used with the machine tool during the machiningoperation.

In order to assure precise alignment and stability of the tool during amachining operation as it, is being moved through a hole, an alignmentassembly, illustrated in FIGS. 2 and 3, is employed. The assemblyincludes a main plate member 50. A pair of threaded elements 52 and 54are welded or otherwise suitably secured to the plate member 50. Thethreaded elements 52 and 54 are spaced so that they may be insertedthrough holes in the drum which are disposed on either side of the holeto be drilled.

The member 50 also includes a central aperture 56 disposed to be alignedwith the hole to be drilled. The aperture 56 is dimensioned to receivean alignment portion of the tool 16 disposed in front of the element 18.

The member 50 is held in place on the drum by means of bolts 60 and 62threadedly engaging the threaded elements 52 and 54, respectively. Apair of washer type elements 64 and 66 larger in area than the holes inthe drum is provided to hold the member 50 when the bolts 60 and 62 aretightened.

When a hole is to be drilled in the drum, the member 50 is secured tothe outer surface of the drum. The tool portion 58 is inserted into theopening 56. This arrangement assures that the drill 18 is maintained inprecise alignment as it performs the drilling operation.

FIG. 2 also illustrates the rotational movement of the tool 16, with thedotted lines 64 illustrating a position of the tool after it has beenmoved a number of holes from a starting position, which is illustratedby the solid lines. FIG. 3 also illustrates the radial movement of thetool 16, with the dotted lines illustrating the position of the tool 16when it is extended into a hole in the drum. FIG. 6 illustrates the tool16 at different longitudinal positions with dotted lines 68 and 70representing the tool in different positions from its original positionillustrated by the solid lines.

After all the holes in the drum have been drilled or bored to the propersize, the tubes may be inserted therein. An expander machine (notillustrated) is used to expand the ends of the tubes to provide a tightmechanical seal against the edges of the holes in a well known manner.

FIGS. 8a, 8b and 8c illustrate another embodiment of the method of thepresent invention. As is illustrated in FIG. 8a, in this embodiment, ahole 17 in a drum is bored to a larger size hole 19, illustrated in FIG.8b. A tapered metal ring 21, with sufficient interference to facilitatea tap fit having substantially the same outside diameter as the hole 19,is then inserted into the hole 19. The ring 21 may be tapped into thehole 19 to fit tightly. This prevents the ring from spinning when it isexpanded. The tapers of the hole 19 and ring 21 extend inwardly from theinterior of the drum, with the narrow portions being towards theexterior of the drum. Thus, pressure within the drum tends to produce abetter sealing effect between the ring and the drum. After insertion,the inner end of the ring 21 is then expanded in a well known manner toprovide a good mechanical seal between the ring and the drum. The tapersof the ring and opening may be in the order of 3 to 5, for example. Theinner diameter of the ring 21 is dimensioned to receive the ends of thereplacement tubes, with the ends of the tubes being expanded to providegood sealing between the tubes and the rings. This method is adaptablein cases were exotic metals are involved and welding is prohibited.

In using the machine tool 16, it is desirable to use a variable speedfor different drilling or boring operations where different size holesor other variable operating conditions are present. FIG. 9 illustratesan electrical circuit wherein a potentiometer or rheostat 23 isconnected across the source of power to control the voltage applied tothe tool 16, thereby controlling the speed thereof; For example, manycommercially boring machines are adapted to operate at 250 rpm. Drillingof relatively large holes requires operation in the order of I00 rpm.The feature of variable speed adds to the versatility of the apparatusdescribed.

A number of additions or changes may be made without departing from thescope of the present invention. For example, hydraulic means may beemployed to perform some of the operations which, in the apparatusillustrated, are manually performed by an operator. The tube includespiston elements connected to the shaft 22, which is adapted to providethe longitudinal movement of the tool 16 described. The centering oralignment means 28 and 30 may also be hydraulically driven to maintainthe tool 16 properly centered. Gauge markings could be associated withthe alignment means, if desired. Various rack and pinion assembliesincluding rams could be provided to provide measured movement of thetool 16 both rotationally and longitudinally. In advanced systems, thevarious steps of the tool 16 may be programmed to produce the desiredoperation and subsequent movements.

While the subject invention has been described in terms of repairing adrum, the apparatus and methods may also be used in the production ofholes in a drum during manufacturing. The disposition of the apparatuswithin a drum facilitates the alignment of machining operations involvedfor both repair and manufacturing.

In some cases, operations in addition to boring and drilling may bedesired, for example, threading or other machining operations may alsobe performed in the holes of a drum by use of the apparatus of thepresent invention. 6

The holes machined in the drum need not be disposed in precise alignmentas illustrated, although this is generally the case in conventionalboiler drums. Sometimes the movement of the tool 16 need only be in onedirection, i.e. either rotated or moved longitudinally, to perform thedesired operation.

The present invention has provided methods and means for repairingboiler drums which heretofore had to be replaced as a result ofelongated holes formed by overheating. This results in considerablesavings in the operation of steam generating plants both in thereplacement equipment and the labor involved in installation of newequipment.

What is claimed is:

l. A method of repairing a cylindrical drum including a plurality ofholes therein extending along a line longitudinally along said drum,said holes having become enlarged or elongated as a result of corrosion,overheating or the like, said method comprising the steps of adding aweld material to said drum in the area of said holes to reducesubstantially the size of said holes and thus provide smaller holes,providing an assembly including a movably mounted tool with a cutterelement larger in dimension than said smaller holes with said tool beingmovable longitudinally on said assembly, fixedly mounting said assemblyinside of said drum in a predetermined position, moving said toolsequentially in steps with said assembly in place longitudinally withinsaid drum to positions in alignment with said smaller holes, andmachining away part of said weld material to produce a set oflongitudinal holes corresponding to the dimensions of said cutterelement.

2. A method as set forth in claim 1, wherein said plurality of holes insaid drum also extend about the circumference of said drum and includingthe additional steps of rotatably mounting said tool in said shaft,rotating said tool within said drum with said assembly in place inalignment with said smaller holes extending about the circumference ofsaid drum, and machining away part of said weld material about thecircumference of said drum to produce holes corresponding to thedimensions of said cutter element.

3. A method as set forth in claim 2, wherein the additional steps areprovided of adjusting the rotational axis of said tool to substantialalignment with the longitudinal axis of said drum.

4. A method as set forth in claim 3, wherein the additional steps areprovided of sequentially drilling an additional set of circumferentiallyspaced holes after moving said tool a predetermined distance after thedrilling of each individual set of holes.

5. A method of repairing a plurality of irregularly shaped damaged holesin a drum comprising the steps of adding a weld material to said drum inthe area of said holes to reduce substantially the size of said holesand thus provide smaller holes, inserting apparatus including a movablymounted machine tool with a cutting element inside of said drum,machining said smaller holes to a circular shape with said apparatus inplace,

inserting metal rings into said circular shaped holes, expanding saidrings to provide tight mechanical seals with said drum, inserting tubesinto said rings, and expanding the ends of said tubes to provide tightmechanical seals with the interior surfaces of said rings.

6. A method of repairing a cylindrical drum having a plurality ofenlarged or elongated holes extending around the circumference of saiddrum, said method comprising the steps of adding a weld material to saiddrum in the area of said holes to reduce substantially the size of saidholes and thus provide smaller holes, providing an assembly including atool with a cutter element larger in dimensions than said smaller holeswith said tool being rotatable on said assembly, fixedly mounting saidassembly within said drum in a predetermined position, rotating saidtool sequentially in steps with said assembly in place within said drumto positions in alignment with said smaller holes, and machining awaypart of said weld material to produce a set of circular holes around thecircumference of said drum corresponding to the dimensions of saidcutter element.

7. A method as set forth in claim 5 wherein the step of machiningcomprises machining the circular holes to have tapered edges and furtherincluding the step of inserting into said circular holes metal ringshaving tapered edges corresponding to the tapers of said circular holes.

l I i

1. A method of repairing a cylindrical drum including a plurality ofholes therein extending along a line longitudinally along said drum,said holes having become enlarged or elongated as a result of corrosion,overheating or the like, said method comprising the steps of adding aweld material to said drum in the area of said holes to reducesubstantially the size of said holes and thus provide smaller holes,providing an assembly including a movably mounted tool with a cutterelement larger in dimension than said smaller holes with said tool beingmovable longiTudinally on said assembly, fixedly mounting said assemblyinside of said drum in a predetermined position, moving said toolsequentially in steps with said assembly in place longitudinally withinsaid drum to positions in alignment with said smaller holes, andmachining away part of said weld material to produce a set oflongitudinal holes corresponding to the dimensions of said cutterelement.
 2. A method as set forth in claim 1, wherein said plurality ofholes in said drum also extend about the circumference of said drum andincluding the additional steps of rotatably mounting said tool in saidshaft, rotating said tool within said drum with said assembly in placein alignment with said smaller holes extending about the circumferenceof said drum, and machining away part of said weld material about thecircumference of said drum to produce holes corresponding to thedimensions of said cutter element.
 3. A method as set forth in claim 2,wherein the additional steps are provided of adjusting the rotationalaxis of said tool to substantial alignment with the longitudinal axis ofsaid drum.
 4. A method as set forth in claim 3, wherein the additionalsteps are provided of sequentially drilling an additional set ofcircumferentially spaced holes after moving said tool a predetermineddistance after the drilling of each individual set of holes.
 5. A methodof repairing a plurality of irregularly shaped damaged holes in a drumcomprising the steps of adding a weld material to said drum in the areaof said holes to reduce substantially the size of said holes and thusprovide smaller holes, inserting apparatus including a movably mountedmachine tool with a cutting element inside of said drum, machining saidsmaller holes to a circular shape with said apparatus in place,inserting metal rings into said circular shaped holes, expanding saidrings to provide tight mechanical seals with said drum, inserting tubesinto said rings, and expanding the ends of said tubes to provide tightmechanical seals with the interior surfaces of said rings.
 6. A methodof repairing a cylindrical drum having a plurality of enlarged orelongated holes extending around the circumference of said drum, saidmethod comprising the steps of adding a weld material to said drum inthe area of said holes to reduce substantially the size of said holesand thus provide smaller holes, providing an assembly including a toolwith a cutter element larger in dimensions than said smaller holes withsaid tool being rotatable on said assembly, fixedly mounting saidassembly within said drum in a predetermined position, rotating saidtool sequentially in steps with said assembly in place within said drumto positions in alignment with said smaller holes, and machining awaypart of said weld material to produce a set of circular holes around thecircumference of said drum corresponding to the dimensions of saidcutter element.
 7. A method as set forth in claim 5 wherein the step ofmachining comprises machining the circular holes to have tapered edgesand further including the step of inserting into said circular holesmetal rings having tapered edges corresponding to the tapers of saidcircular holes.